Method for providing a hermetically sealed feedthrough with co-fired filled via for an active implantable medical device

ABSTRACT

A method for making a dielectric substrate configured for incorporation into a hermetically sealed feedthrough is described. The method includes forming a via hole through a green-state dielectric substrate. A platinum-containing paste is filled into at least 90% of the volume of the via hole. The green-state dielectric substrate is then subjected to a heating protocol including: a binder bake-out heating portion performed at a temperature ranging from about 400° C. to about 700° C. for a minimum of 4 hours; a sintering heating portion performed at a temperature ranging from about 1,400° C. to about 1,900° C. for up to 6 hours; and a cool down portion at a rate of up to 5°/minute from a maximum sintering temperature down to about 1,000° C., then naturally to room temperature. The thusly manufacture dielectric substrate is then positioned in an opening in a ferrule that is configured to be attached to a metal housing of an active implantable medical device. The dielectric substrate is hermetically sealed to the ferrule with the sintered platinum material in the via hole providing a conductive pathway from a body fluid side to a device side of the ferrule.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.15/894,239, filed on Feb. 12, 2018, now U.S. Pat. No. 10,500,402, whichis a continuation of application Ser. No. 14/797,123, filed on Jul. 11,2015, now U.S. Pat. No. 9,889,306, which is a continuation-in-part ofapplication Ser. No. 14/182,569, filed on Feb. 18, 2014, now U.S. Pat.No. 9,492,659, which is a divisional of application Ser. No. 13/743,254,filed on Jan. 16, 2013, now U.S. Pat. No. 8,653,384, which claimspriority to provisional application Ser. No. 61/587,029, filed on Jan.16, 2012; 61/587,287, filed on Jan. 17, 2012; and 61/587,373, filed onJan. 17, 2012. The contents of all the above-mentioned applications areherein incorporated in full by these references.

FIELD OF THE INVENTION

The present invention generally relates to implantable medical devicesand hermetic terminal subassemblies. More particularly, the presentinvention relates to a hermetic terminal subassembly utilizing aco-fired essentially pure platinum filled via along with novel ways ofmaking electrical connections on the body fluid and device side of theactive implantable medical device (AIMD) housing.

BACKGROUND OF THE INVENTION

A wide assortment of active implantable medical devices (AIMD) arepresently known and in commercial use. Such devices include cardiacpacemakers, cardiac defibrillators, cardioverters, neurostimulators, andother devices for delivering and/or receiving electrical signals to/froma portion of the body. Sensing and/or stimulating leads extend from theassociated implantable medical device to a distal tip electrode orelectrodes in contact with body tissue.

The hermetic terminal or feedthrough of these implantable devices isconsidered critical. Hermetic terminals or feedthroughs are generallywell-known in the art for connecting electrical signals through thehousing or case of an AIMD. For example, in implantable medical devicessuch as cardiac pacemakers, implantable cardioverter defibrillators, andthe like, a hermetic terminal comprises one or more conductive terminalpins supported by an insulative structure for feedthrough passage fromthe exterior to the interior of an AIMD electromagnetic shield housing.Hermetic terminals or feedthroughs for AIMDs must be biocompatible aswell as resistant to degradation under applied bias current or voltage.Hermeticity of the feedthrough is imparted by judicious materialselection and carefully prescribed manufacturing processing. Sustainablehermeticity of the feedthrough over the lifetime of these implantabledevices is critical because the hermetic terminal intentionally isolatesthe internal circuitry and components of the device from the externalenvironment to which the component is exposed. In particular, thehermetic terminal isolates the internal circuitry, connections, powersources and other components in the device from ingress of body fluids.Ingress of body fluids into an implantable medical device is known to bea contributing factor to device malfunction and may contribute to thecompromise or failure of electrical circuitry, connections, powersources and other components within an implantable medical device thatare necessary for consistent and reliable device therapy delivery to apatient. Furthermore, ingress of body fluids may compromise animplantable medical device's functionality which may constituteelectrical shorting, element or joint corrosion, metal migration orother such harmful consequences affecting consistent and reliable devicetherapy delivery.

In addition to concerns relative to sustained terminal or feedthroughhermeticity, other potentially compromising conditions must beaddressed, particularly when a hermetic terminal or feedthrough isincorporated within an implantable medical device. For example, thehermetic terminal or feedthrough pins are typically connected to one ormore leadwires of implantable therapy delivery leads. These implantabletherapy delivery leads can effectively act as antennas ofelectromagnetic interference (EMI) signals. Therefore, when theseelectromagnetic signals enter within the interior space of a hermeticimplantable medical device, facilitated by the therapy delivery leads,they can negatively impact the intended function of the medical deviceand as a result, negatively impact therapy delivery intended for apatient by that device. EMI engineers commonly refer to this as the“genie in the bottle” effect. In other words, once the genie (i.e., EMI)is inside the hermetic device, it can wreak havoc with electroniccircuit functions by cross-coupling and re-radiating within the device.

Another particularly problematic condition associated with implantedtherapy delivery leads occurs when a patient is in an MRI environment.In this case, the electrical currents imposed on the implanted therapydelivery leads can cause the leads to heat to the point where tissuedamage is likely. Moreover, the electrical currents developed in theseimplanted therapy delivery leads during an MRI procedure can disrupt ordamage the sensitive electronics within the implantable medical device.

Therefore, materials selection and fabrication processing parameters areof utmost importance in creating a hermetic terminal (or feedthrough) ora structure embodying a hermetic terminal (or feedthrough), that cansurvive anticipated and possibly catastrophically damaging environmentalconditions and that can be practically and cost effectivelymanufactured.

Hermetic terminals or feedthrough assemblies utilizing ceramicdielectric materials may fail in a brittle manner. A brittle failuretypically occurs when the ceramic structure is deformed elastically upto an intolerable stress, at which point the ceramic failscatastrophically. Virtually all brittle failures occur by crackpropagation in a tensile stress field. Even microcracking caused bysufficiently high tensile stress concentrations may result in acatastrophic failure including loss of hermeticity identified ascritical in hermetic terminals for implantable medical devices. Loss ofhermeticity may be a result of design aspects such as a sharp cornerwhich creates a stress riser, mating materials with a difference ofcoefficient of thermal expansions (CTE) that generate tensile stressesthat ultimately result in loss of hermeticity of the feedthrough orinterconnect structure.

In the specific case of hermetic terminal or feedthrough designs, atensile stress limit for a given ceramic based hermetic design structurecannot be specified because failure stress in these structures is not aconstant. As indicated above, variables affecting stress levels includethe design itself, the materials selection, symmetry of the feedthrough,and the bonding characteristics of mating surfaces within thefeedthrough. Hence, length, width and height of the overall ceramicstructure matters as do the number, spacing, length and diameter of thevias in that structure. The selection of the mating materials, that is,the material that fills the vias and the material that forms the baseceramic, are important. Finally, the fabrication processing parameters,particularly at binder burnout, sintering and cool down, make adifference. When high reliability is required in an application such asindicated with hermetic terminals or feedthroughs for AIMDs, to provideensurance for a very low probability of failure it is necessary todesign a hermetic terminal assembly or feedthrough structure so thatstresses imparted by design, materials and/or processing are limited toa smaller level of an average possible failure stress. Further, toprovide ensurance for a very low probability of failure in a criticalceramic based assembly or subassembly having sustainable hermeticrequirements, it is also necessary to design structures embodying ahermetic terminal or feedthrough such that stresses in the finalassembly or subassembly are limited to a smaller level of an averagepossible failure stress for the entire assembly or subassembly. Inhermetic terminals and structures comprising hermetic terminals forAIMDs wherein the demand for biocompatibility exists, this task becomeseven more difficult.

The most critical feature of a feedthrough design or any terminalsubassembly is the metal/ceramic interface within the feedthrough thatestablishes the hermetic seal. The present invention therefore, providesa hermetic feedthrough comprising a monolithic alumina insulatorsubstrate within which a platinum conductive pathway or via resides.More specifically, the present invention provides a hermetic feedthroughin which the hermetic seal is created through the intimate bonding ofthe platinum metal residing within the alumina substrate.

A traditional ceramic-to-metal hermetic terminal is an assembly of threecomponents: metal leadwires that conduct electrical current, a ceramicinsulator, and a metal housing, which is referred to as the flange orthe ferrule. Brazed joints hermetically seal the metal leadwires and theflange or ferrule to the ceramic insulator. For a braze-bonded joint,the braze material is generally intended to deform in a ductile mannerin order to compensate for perturbations that stress the bond betweenthe mating materials as the braze material may provide ductile strainrelief when the thermal expansion mismatch between the ceramic and metalis large. Thus, mating materials with large mismatches in CTE can becoupled through braze materials whose high creep rate and low yieldstrength reduce the stresses generated by the differential contractionexisting between these mating materials.

Thermal expansion of metal is generally considerably greater than thoseof ceramics. Hence, successfully creating a hermetic structure, and onethat can sustain its hermeticity in service, is challenging due to thelevel of residual stresses in the final structure. Specifically, thermalexpansion mismatch results in stresses acting along the ceramic/metalinterface that tend to separate the ceramic from the metal and so thebond developed between the ceramic and the metal must be of sufficientstrength to withstand these stresses, otherwise adherence failure, thatis, loss of hermeticity, will occur. One method for limiting thesestresses is to select combinations of materials whose thermalcontractions after bonding are matched.

In making the selection for a CTE match, it is important to note thatvery few pairs of materials have essentially identical thermal expansioncurves. Generally, the metal component is selected first based onelectrical and thermal conductivity, thermal expansion, ability to bewelded or soldered, mechanical strength, and chemical resistance orbiocompatibility requirements; the ceramic is then selected basedprimarily on electrical resistivity, dielectric strength, low gaspermeability, environmental stability, and thermal expansioncharacteristics. In the specific case of selecting platinum wire, oftenthe ceramic formulation is modified in order to match its CTE to that ofthe platinum wire. In yet a more specific case of selecting platinumpaste, the platinum paste formulation may be modified as well. If themating materials are alumina of at least 96% purity and essentially pureplatinum paste, then matching CTE is not possible. Thus, for AIMD's,consistently achieving hermetic terminal structures that are capable ofsustaining hermeticity throughout the application's service life hasproven challenging.

Producing a stress-free structure often not only involves bonding a pairof materials but also achieving that bond at a very specific temperatureso that their contractions on cooling to room temperature areessentially the same even though the contraction curves may notcoincide. Since this often is a significant challenge, hermeticterminals are produced by metalizing the alumina and using a brazingmaterial to form the bond at some other temperature than an intersectionof the CTE curves. (NOTE: Forming a bond between two materials thatbecome rigid at the intersection of the two CTE curves makes it possibleto produce a structure that is stress free at room temperature, unlessthe two CTE curves separate substantially from each other from theintersection point and room temperature.) The deformation of the brazematerial by time-independent plastic flow or creep relaxation limits thestresses generated in the ceramic. Given this, the impact of the rate ofcooling on the final stress level of a structure must also beconsidered. In some cases, residual stresses are generated deliberatelyto provide protective compressive stresses in the ceramic part and inthe bond interface. Usually this is accomplished by selecting componentswith different CTEs. Another way is to control the shrinkage of onematerial over its mating material. In either case, it is important tominimize stress levels such that the interface on which hermeticitydepends is well within the stress level at which failure might occur.

In an embodiment, the present invention is directed to mating boundparticulate high purity alumina of at least 96% and particles ofessentially pure platinum metal that are suspended within a mixture ofsolvents and binders, i.e. a platinum paste. This combination ofmaterials does not use a braze material to buffer the CTE mismatchbetween these two materials. Further, since the intent of this inventionis to provide hermetic terminals and subassemblies comprising hermeticterminals for AIMDs, the present invention does not considermodifications to the alumina formulation or the platinum paste in anattempt to match their CTEs. Rather, this invention disclosessustainable hermetic terminals and structures embodying these hermeticterminals. This is achieved by adjusting platinum paste solids loading,prescribing via packing, prescribing binder burnout, sintering and cooldown parameters, such that shrinkage of the alumina is greater than theshrinkage of the platinum fill in the via and an intimate and tortuous(a mutually conformal) interface is created that may be either a directbond between the alumina and platinum materials that is hermetic.Alternatively, or that may develop an amorphous interfacial layer thatis not susceptible to erosion by body fluids and can tolerate stresslevels without losing hermeticity.

Regarding EMI, a terminal or feedthrough capacitor EMI filter may bedisposed at, near or within a hermetic terminal or feedthrough resultingin a feedthrough filter capacitor which diverts high frequencyelectrical signals from lead conductors to the housing or case of anAIMD. Many different insulator structures and related mounting methodsare known in the art for use of feedthrough capacitor EMI filters inAIMDs, wherein the insulative structure also provides a hermeticterminal or feedthrough to prevent entry of body fluids into the housingof an AIMD. In the prior art devices, the hermetic terminal subassemblyhas been combined in various ways with a ceramic feedthrough filter EMIcapacitor to decouple interference signals to the housing of the medicaldevice.

In a typical prior art unipolar construction (as described in U.S. Pat.No. 5,333,095 and herein incorporated by reference), a round/discoidal(or rectangular) ceramic feedthrough EMI filter capacitor is combinedwith a hermetic terminal pin assembly to suppress and decouple undesiredinterference or noise transmission along a terminal pin. The feedthroughcapacitor is coaxial having two sets of electrode plates embedded inspaced relation within an insulative dielectric substrate or base,formed typically as a ceramic monolithic structure. One set of theelectrode plates are electrically connected at an inner diametercylindrical surface of the coaxial capacitor structure to the conductiveterminal pin utilized to pass the desired electrical signal or signals.The other or second set of electrode plates are coupled at an outerdiameter surface of the round/discoidal capacitor to a cylindricalferrule of conductive material, wherein the ferrule is electricallyconnected in turn to the conductive housing of the electronic device.The number and dielectric thickness spacing of the electrode plate setsvaries in accordance with the capacitance value and the voltage ratingof the coaxial capacitor. The outer feedthrough capacitor electrodeplate sets (or “ground” plates) are coupled in parallel together by ametalized layer which is either fired, sputtered or plated onto theceramic capacitor. This metalized band, in turn, is coupled to theferrule by conductive adhesive, soldering, brazing, welding, or thelike. The inner feedthrough capacitor electrode plate sets (or “active”plates) are coupled in parallel together by a metalized layer which iseither glass frit fired or plated onto the ceramic capacitor. Thismetalized band, in turn, is mechanically and electrically coupled to thelead wire(s) by conductive adhesive, soldering, or the like. Inoperation, the coaxial capacitor permits passage of relatively lowfrequency biologic signals along the terminal pin, while shielding anddecoupling/attenuating undesired interference signals of typically highfrequency to the AIMD conductive housing. Feedthrough capacitors of thisgeneral type are available in unipolar (one), bipolar (two), tripolar(three), quadpolar (four), pentapolar (five), hexpolar (6) andadditional lead configurations. The feedthrough capacitors (in bothdiscoidal and rectangular configurations) of this general type arecommonly employed in implantable cardiac pacemakers and defibrillatorsand the like, wherein the pacemaker housing is constructed from abiocompatible metal such as titanium alloy, which is electrically andmechanically coupled to the ferrule of the hermetic terminal pinassembly which is in turn electrically coupled to the coaxialfeedthrough filter capacitor. As a result, the filter capacitor andterminal pin assembly prevents entrance of interference signals to theinterior of the pacemaker housing, wherein such interference signalscould otherwise adversely affect the desired cardiac pacing ordefibrillation function.

Regarding MRI related issues, bandstop filters, such as those describedin U.S. Pat. No. 6,008,980, which is herein incorporated by reference,reduce or eliminate the transmission of damaging frequencies along theleads while allowing the desired biologic frequencies to passefficiently through.

Referring once again to feedthrough capacitor EMI filter assemblies,although these assemblies as described earlier have performed in agenerally satisfactory manner, and notwithstanding that the associatedmanufacturing and assembly costs are unacceptably high in that thechoice of the dielectric material for the capacitor has significantimpacts on cost and final performance of the feedthrough filtercapacitor, alumina ceramic has not been used in the past as thedielectric material for AIMD feedthrough capacitors. Alumina ceramic isstructurally strong and biocompatible with body fluids but has adielectric constant around 6 (less than 10). There are other moreeffective dielectric materials available for use in feedthrough filtercapacitor designs. Relatively high dielectric constant materials (forexample, barium titanate with a dielectric constant of over 2,000) aretraditionally used to manufacture AIMD feedthrough capacitors forintegrated ceramic capacitors and hermetic seals resulting in moreeffective capacitor designs. Yet ceramic dielectric materials such asbarium titanate are not as strong as the alumina ceramic typically usedto manufacture the hermetic seal subassembly in the prior art. Bariumtitanate is also not biocompatible with body fluids. Direct assembly ofthe ceramic capacitor can result in intolerable stress levels to thecapacitor due to the mismatch in thermal coefficients of expansionbetween the titanium pacemaker housing (or other metallic structures)and the capacitor dielectric. Hence, particular care must be used toavoid cracking of the capacitor element. Accordingly, the use ofdielectric materials with a low dielectric constant and a relativelyhigh modulus of toughness are desirable yet still difficult to achievefor capacitance-efficient designs.

Therefore, it is very common in the prior art to construct a hermeticterminal subassembly with a feedthrough capacitor attached near theinside of the AIMD housing on the device side. The feedthrough capacitordoes not have to be made from biocompatible materials because it islocated on the device side inside the AIMD housing. The hermeticterminal subassembly allows leadwires to hermetically pass through theinsulator in non-conductive relation with the ferrule or the AIMDhousing. The leadwires also pass through the feedthrough capacitor tothe inside of the AIMD housing. These leadwires are typically continuousand must be biocompatible and non-toxic. Generally, these leadwires areconstructed of platinum or platinum-iridium, palladium orpalladium-iridium, niobium or the like. Platinum-iridium is an idealchoice because it is biocompatible, non-toxic and is also mechanicallyvery strong. The iridium is added to enhance material stiffness and toenable the hermetic terminal subassembly leadwire to sustain bendingstresses. An issue with the use of platinum for leadwires is thatplatinum has become extremely expensive and may be subject to prematurefracture under rigorous processing such as ultrasonic cleaning orapplication use/misuse, possibly unintentional damaging forces resultingfrom Twiddler's Syndrome.

Accordingly, what is needed is a filtered structure like a hermeticterminal or feedthrough, any subassembly made using same and anyfeedthrough filter EMI capacitor assembly which minimizes intolerablestress levels, allows use of preferred materials for AIMDS andeliminates high-priced, platinum, platinum-iridium or equivalent noblemetal hermetic terminal subassembly leadwires. Also, what is needed isan efficient, simple and robust way to connect the leadwires in a headerblock to the novel hermetic terminal subassembly. Correspondingly, it isalso needed to make a similar efficient, simple and robust electricalconnection between the electronics on the device side of the AIMD to thefeedthrough capacitor and hermetic terminal subassembly. The presentinvention fulfills these needs and provides other related advantages.

SUMMARY OF THE INVENTION

An exemplary embodiment of a hermetically sealed feedthrough forattachment to an active implantable medical device includes a dielectricsubstrate configured to be hermetically sealed to a ferrule or an AIMDhousing. A via hole is disposed through the dielectric substrate from abody fluid side to a device side. A conductive fill is disposed withinthe via hole forming a filled via electrically conductive between thebody fluid side and the device side. A conductive insert is at leastpartially disposed within the conductive fill. The conductive fill andthe conductive insert are co-fired with the dielectric substrate to forma hermetically sealed and electrically conductive pathway through thedielectric substrate between the body fluid side and the device side.

In other exemplary embodiments the conductive fill may include asubstantially closed pore and substantially pure metallic fill. Theconductive insert may include a substantially pure metallic insert,where the metallic insert and the metallic fill are of the same metallicmaterial type. An inherent shrink rate during a co-firing treatment ofthe dielectric substrate in a green state may be greater than that of aninherent shrink rate during the co-firing treatment of the metallic fillin a green state.

In other exemplary embodiments the conductive fill may include asubstantially closed pore and substantially pure platinum fill. Theconductive insert may include a substantially pure platinum insert. Thedielectric substrate may include an alumina substrate comprised of atleast 96 percent alumina. The hermetically sealed and electricallyconductive pathway may include a first hermetic seal between theplatinum fill and the alumina dielectric substrate, wherein the platinumfill forms a tortuous and mutually conformal knitline or interfacebetween the alumina substrate and the platinum fill. The hermeticallysealed and electrically conductive pathway may include a second hermeticseal between the platinum fill and the platinum insert, wherein theplatinum fill forms a second tortuous and mutually conformal knitline orinterface between the platinum fill and the platinum insert. At least aportion of an outer surface of the platinum insert may be forming thesecond tortuous and mutually conformal knitline or interface comprises asubstantially irregular surface.

The conductive insert may be exposed through the conductive fill on thebody fluid side or the device side of the dielectric substrate. Theconductive insert may be flush with a device side surface or a bodyfluid side surface of the dielectric substrate. The conductive insertmay extend beyond a device side surface or a body fluid side surface ofthe dielectric substrate. The conductive insert may include an enlargedend cap on the device side or the body fluid side of the dielectricsubstrate. The conductive insert may include a first portion separateand distinct from a second portion, where the first and second portionsare configured to abut one another when disposed from opposite sides ofthe body fluid side and the device side through the conductive fill.

The conductive insert may include a crimp post extending beyond a deviceside surface or a body fluid side surface of the dielectric substrate.The crimp post may include a receptacle configured to receive aconductive wire, wherein the crimp post comprises a cross-sectionalshape of a circle, an oval, a rectangle or a square. The crimp post mayinclude at least one slot at least partially disposed along alongitudinal length of the crimp post. The at least one slot may befully disposed along the longitudinal length of the crimp post.

A feedthrough capacitor may be disposed on the device side of thedielectric substrate, the feedthrough capacitor comprising at least oneactive electrode plate separated from at least one ground electrodeplate by a capacitor dielectric, wherein the at least one activeelectrode plate is electrically coupled to the conductive pathway andwherein the at least one ground electric plate is electrically coupledto the ferrule or AIMD housing, wherein the feedthrough capacitor formsa frequency selective diverter circuit between the conductive pathwayand to the ferrule or AIMD housing.

A circuit board may be disposed on the device side of the dielectricsubstrate, wherein the circuit board comprises at least one monolithicchip capacitor (MLCC) electrically coupled between the conductivepathway and to the ferrule or AIMD housing, where the MLCC forms afrequency selective diverter circuit between the conductive pathway andto the ferrule or AIMD housing.

A shielded three-terminal flat-through EMI energy dissipating filter maybe disposed on the device side of the dielectric substrate, theflat-through filter comprising: i) at least one active electrode platethrough which a circuit current is configured to pass between a firstterminal and a second terminal; ii) at least one first shield platedisposed on a first side of the at least one active electrode plate; andiii) at least one second shield plate disposed on a second side of theat least one active electrode plate, where the at least one secondshield plate is disposed opposite the at least one first shield plate;iv) wherein the at least one first and second shield plates are bothelectrically coupled to a third terminal, where the third terminal isconfigured to be electrically coupled directly or indirectly to theferrule or the AIMD housing; v) wherein the conductive pathway iselectrically coupled directly or indirectly to the at least one activeelectrode plate and where the conductive pathway is in non-conductiverelationship to the at least one first and second shield plates, theferrule and the AIMD housing.

The conductive insert may include titanium, platinum, platinum-iridiumalloys, tantalum, niobium, zirconium, hafnium, nitinol, Co—Cr—Ni alloys,stainless steel, gold, gold alloys, ZrC, ZrN, TiN, NbO, TiC or TaC.

The receptacle of the crimp post may be disposed perpendicular to alongitudinal length of the crimp post. Alternatively, the receptacle ofthe crimp post may be aligned with a longitudinal length of the crimppost.

The conductive fill may have a larger cross-sectional area at the deviceside or body fluid side as compared to a center portion of theconductive fill.

Other features and advantages of the present invention will becomeapparent from the following more detailed description, when taken inconjunction with the accompanying drawings, which illustrate, by way ofexample, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate the invention. In such drawings:

FIG. 1 is a wire-formed diagram of a generic human body showing a numberof exemplary implantable medical devices;

FIG. 2 is a sectional view of a hermetic insulator with a solid metallicfilled via in a green state;

FIG. 3 is a sectional view of the structure of FIG. 2 now aftersintering;

FIG. 4 is an enlarged view taken from FIG. 3 along lines 4-4 now showinggaps between the solid metallic leadwire and the insulator;

FIG. 5 is a flow chart illustrating the main steps of one embodiment ofthe process of the present invention;

FIG. 6 is a sectional view of a feedthrough assembly now showing a wirebond cap co-fired into the platinum filled via;

FIG. 7 is a sectional view of another feedthrough assembly with acapacitor mounted on the device side;

FIG. 8 is a sectional view taken from FIG. 7 along lines 8-8 now showingthe active plates;

FIG. 9 is a sectional view taken from FIG. 7 along lines 9-9 now showingthe ground plates;

FIG. 10 is a perspective view of an exemplary embodiment of a round quadpolar hermetic terminal assembly;

FIG. 11 is a perspective view of an exemplary wire bond pad;

FIG. 12 is a perspective view of another exemplary wire bond pad;

FIG. 13 is a perspective view of another exemplary wire bond pad;

FIG. 14 is a perspective view of another exemplary wire bond pad;

FIG. 15 is a perspective view of another exemplary embodiment of arectangular hermetic terminal subassembly showing castellations;

FIG. 16 is a perspective view of an embodiment of a wire bond pad;

FIG. 17 is another perspective view of the embodiment of wire bond padin FIG. 16;

FIG. 18 is a sectional view of the structure of FIG. 17 taken alonglines 18-18;

FIG. 19 is an enlarged sectional view of the wire bond pad of FIGS.16-18 co-fired into the platinum filled via;

FIG. 20 is a perspective view of another embodiment of a wire bond padwith attachment fingers;

FIG. 21 is another perspective view of the embodiment of wire bond padin FIG. 20;

FIG. 22 is an enlarged sectional view of another embodiment of a wirebond pad with a pin co-fired into the platinum filled via;

FIG. 23 is an enlarged sectional view of another embodiment of a wirebond pad similar to FIG. 55 now showing a hole to capture the leadwire;

FIG. 24 is a sectional view of another exemplary embodiment of ahermetic terminal subassembly now showing a solid wire co-fired into theplatinum filled via;

FIG. 25 is a sectional view similar to FIG. 24 now showing a staggeredvia hole with a solid wire co-fired into the platinum filled via;

FIG. 26 is a sectional view of an exemplary embodiment of a crimp postco-fired into the platinum filled via;

FIG. 27 is a sectional view of an exemplary embodiment of a double crimppost co-fired into the platinum filled via;

FIG. 28 is a perspective view of an exemplary embodiment of a novelmethod of header block connector assembly attachment showing a supportstructure behind the wire bond pads;

FIG. 29 is a perspective view of a wire bond pad similar to FIG. 28 nowwith a novel slot;

FIG. 30 is a sectional view with a novel crimp post co-fired into theplatinum filled via;

FIG. 31 is a perspective view of another exemplary embodiment of a novelcrimp post similar to FIG. 30;

FIG. 32 is a perspective view of another exemplary embodiment of a novelcrimp post similar to FIG. 30;

FIG. 33 is a perspective view of another exemplary embodiment of a novelcrimp post similar to FIG. 30;

FIG. 34 is a perspective view of another exemplary embodiment of a novelcrimp post similar to FIG. 30;

FIG. 35 is a perspective view of another exemplary embodiment of a novelcrimp post similar to FIG. 30;

FIG. 36 is a perspective view of a hermetic seal sub-assembly shownlaser welded into an opening in the housing of an active implantablemedical device;

FIG. 37 shows the device side of a hermetic terminal sub-assembly nowshown on top;

FIG. 38 is a sectional view taken generally from section 38-38 of FIG.36;

FIG. 39 is a sectional view taken generally from section 39-39 from FIG.36;

FIG. 40 is very similar to FIG. 38 except that in this case, theconductive inserts can be extended a considerable distance above orbelow the entire hermetic seal sub-assembly;

FIG. 41 is an enlarged view taken from the section at lines 41-41 fromFIG. 40;

FIG. 42 is an enlarged view taken from the section at lines 42-42 fromFIG. 41;

FIG. 43 is an enlarged view taken from the section at lines 43-43 fromFIG. 41,

FIG. 44 is very similar to FIG. 41 except that the conductive insert issurrounded by a plating, a coating or a cladding material;

FIG. 45 is very similar to FIGS. 36-38 and is taken generally fromsection 45-45 from FIG. 36, except that now the conductive inserts havea nail head feature;

FIG. 46 is very similar to FIGS. 45 and 36-38 and is taken generallyfrom section 46-46 from FIG. 36, except now shows a nail head feature onthe top and bottom;

FIG. 47 is similar to FIG. 36 except that now the conductive inserts arein the form of hollow tubelets;

FIG. 48 shows the hermetic terminal assembly of FIG. 47 now with a crimppost inverted so one can see the device side on top;

FIG. 49 is a sectional view taken generally from section 49-49 from FIG.47;

FIG. 50 is a sectional view taken generally from section 50-50 from FIG.47;

FIG. 51 is very similar to FIG. 49 except in this case, there are crimpposts positioned on both the body fluid side and the device side;

FIG. 52 is very similar to FIG. 50, now with a crimp post on both thebody fluid side and the device side;

FIG. 53 is very similar to FIG. 52 except in this case, there is a slitalong the edge of the crimp post;

FIG. 54 shows the hermetic seal with the slotted crimp post of FIG. 53inverted;

FIG. 55 is taken from section 55-55 from FIG. 53 showing the slottedcrimp post in side view;

FIG. 56 is taken from section 56-56 from FIG. 53 again showing theslotted crimp post;

FIG. 57 is very similar to FIG. 53 except that the crimp post has doubleslots;

FIG. 58 is the inverted view of the structure from FIG. 57;

FIG. 59 is taken from section 59-59 from FIG. 57 showing the doubleslotted crimp post in half section;

FIG. 60 is taken from section 60-60 from FIG. 57 right through thecenter of the device, this time going through the center of both slots;

FIG. 61 is a perspective view showing one embodiment of a crimp post;

FIG. 61A is a sectional view of the structure of FIG. 61 taken alonglines 61A-61A;

FIG. 62 shows another embodiment of a crimp post with two slots;

FIG. 62A is a sectional view of the structure of FIG. 62 taken alonglines 62A-62A;

FIG. 63 shows another embodiment of a crimp post with three slots;

FIG. 63A is a sectional view of the structure of FIG. 63 taken alonglines 63A-63A;

FIG. 64 shows another embodiment of an oval crimp post;

FIG. 64A is a sectional view of the structure of FIG. 64 taken alonglines 64A-64A;

FIG. 65 shows another embodiment of a rectangular or square crimp post;

FIG. 65A is a sectional view of the structure of FIG. 65 taken alonglines 65A-65A;

FIG. 66 shows an embodiment of a hermetical terminal assembly which hasa single slot in the crimp post;

FIG. 67 shows the perspective view of FIG. 66 inverted so one can seethe device side;

FIG. 68 is taken from section 68-68 from FIG. 66 illustrating that theslotted crimp post extending all the way through the conductive filledvia from the body fluid side to the device side;

FIG. 69 is taken from section 69-69 from FIG. 67 again, illustrating howthe conductive fill penetrates both the outside and the inside diameterof the crimp post;

FIG. 70A shows a sectional view through one embodiment of a crimp postwith one slot;

FIG. 70B shows a sectional view through another embodiment of a crimppost with two halves;

FIG. 70C shows a sectional view through another embodiment of a crimppost with three sections;

FIG. 70D shows a sectional view through another embodiment of a crimppost with four sections;

FIG. 70E shows a sectional view through another embodiment of an ovalcrimp post with one slot;

FIG. 70F shows a sectional view through another embodiment of a squarecrimp post having four parts;

FIG. 71 illustrates that any of the novel hermetic seals of the presentinvention can have a device side mounted feedthrough capacitor; and

FIG. 72 illustrates an alternative filter embodiment in comparison toFIG. 71, wherein a circuit substrate has been placed over the five crimpposts with individual MLCC chip capacitors.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates various types of active implantable and externalmedical devices 100 that are currently in use. FIG. 1 is a wire formeddiagram of a generic human body showing a number of implanted medicaldevices. 100A is a family of external and implantable hearing deviceswhich can include the group of hearing aids, cochlear implants,piezoelectric sound bridge transducers and the like. 1008 includes anentire variety of neurostimulators and brain stimulators.Neurostimulators are used to stimulate the Vagus nerve, for example, totreat epilepsy, obesity and depression. Brain stimulators are similar toa pacemaker-like device and include electrodes implanted deep into thebrain for sensing the onset of a seizure and also providing electricalstimulation to brain tissue to prevent the seizure from actuallyhappening. The lead wires that come from a deep brain stimulator areoften placed using real time imaging. Most commonly such lead wires areplaced during real time MRI. 100C shows a cardiac pacemaker which iswell-known in the art. 100D includes the family of left ventricularassist devices (LVAD's), and artificial hearts, including the recentlyintroduced artificial heart known as the Abiocor. 100E includes anentire family of drug pumps which can be used for dispensing of insulin,chemotherapy drugs, pain medications and the like. Insulin pumps areevolving from passive devices to ones that have sensors and closed loopsystems. That is, real time monitoring of blood sugar levels will occur.These devices tend to be more sensitive to EMI than passive pumps thathave no sense circuitry or externally implanted lead wires. 100Fincludes a variety of external or implantable bone growth stimulatorsfor rapid healing of fractures. 100G includes urinary incontinencedevices. 100H includes the family of pain relief spinal cord stimulatorsand anti-tremor stimulators. 100H also includes an entire family ofother types of neurostimulators used to block pain. 1001 includes afamily of implantable cardioverter defibrillators (ICD) devices and alsoincludes the family of congestive heart failure devices (CHF). This isalso known in the art as cardio resynchronization therapy devices,otherwise known as CRT devices. 100J illustrates an externally wornpack. This pack could be an external insulin pump, an external drugpump, an external neurostimulator, a Holter monitor with skin electrodesor even a ventricular assist device power pack. 100K illustrates theinsertion of an external probe or catheter. These probes can be insertedinto the femoral artery, for example, or in any other number oflocations in the human body.

As used herein, the term “lead” refers to an implantable lead containinga lead body and one or more internal lead conductors. A “lead conductor”refers to the conductor that is inside of an implanted lead body. Asused herein, the term “leadwire” refers to wiring that is either insideof the active implantable medical device (AIMD) housing or inside of theAIMD header block assembly or both. As used herein, the term headerblock is the biocompatible material that attaches between the AIMDhousing and the lead. The term header block connector assembly refers tothe header block including the connector ports for the leads and thewiring connecting the lead connector ports to the hermetic terminalsubassemblies which allow electrical connections to hermetically passinside the device housing. It is also understood by those skilled in theart that the present invention can be applicable to active implantablemedical devices that do not have a header block or header blockconnector assemblies such as pulse generators.

It is understood that “vias” are defined as holes, apertures, conduits,or voids created in either insulators or capacitors. A via can also befilled with a conductive material or bore-coated with a conductivematerial such that the inside surface is metalized and conductivelycoated. A via in a capacitor will generally be referred to as acapacitor via. A via in an insulator will generally be referred to as aninsulator via. Accordingly, the terms filled or bore-coated can also beapplied to either capacitor vias or insulator vias.

FIG. 2 illustrates a prior art cross-section of a different type ofhermetic terminal subassembly substrate. The insulator 120 is a ceramicsubstrate formed by roll compaction. After compaction, the leadwire 180is placed within the insulator via. In this case, the insulator via isfilled with a solid platinum leadwire 180. FIG. 4 is an enlarged viewtaken from FIG. 3 showing gaps 182 that are created between theinsulator 120 and the leadwire 180. These gaps reduce hermeticity andare very problematic.

One is referred to U.S. Pat. Nos. 7,480,988; 7,989,080; and 8,163,397.These three patents share a common priority chain and are directed to amethod and apparatus for providing a hermetic electrical feedthrough.All three of these patents were assigned to Second Sight MedicalProducts, Inc. and will hereinafter be referred to as the “Second Sight”patents. FIG. 3 of the Second Sight patents is a flow process thatstarts with drilling blind holes in a green ceramic sheet. Then lengthsof platinum leadwire 180 are cut and inserted into the sheet holes instep 39. The ceramic wire assembly is then fired at 1600° C. in step 44.Second Sight discloses that “during the firing and subsequent cooling,the ceramic expands shrinking the holes around the wires 38 to form acompression seal. The shrinkage is believed to occur, at least in part,as a consequence of polymer binder burnout. The fine aluminum oxidesuspension permits uniform and continuous sealing around the surface ofthe wire. Additionally, at the maximum firing temperature, e.g., 1600°C., the solid platinum wires being squeezed by the ceramic exhibitsufficient plasticity to enable the platinum to flow and fill anycrevices. This action produces a hermetic metal/ceramic interface.”Further, Second Sight discusses that “After lapping, the feedthroughassembly comprised of the finished ceramic sheet and feedthrough wires,is subjected to a hermeticity test, e.g., frequently a helium leak testas represented by block 56 in FIG. 3.” While Second Sight discussesforming a compression seal and platinum flow to fill any crevices,creation of mutually conformal interface or tortuous, intimate knitlinebetween the alumina and the platinum wire is not taught.

In addition, latent hermetic failures in device feedthrough terminalshave been known to occur due to susceptibility of the glass phasedinterface between these mating materials to erosion by body fluids. Thisoutcome is particularly prevalent for interfaces comprising silicateglasses that are often a result of the additives to ceramic slurriesforming the tapes and via fill materials that are used to buildmultilayer ceramic feedthrough structures. Dissolution of silicateglasses is composition dependent. In particular, erosion of silicateglasses in the body typically occurs when the silica content is lowerthan about 60%. Silica glasses, as suggested by the name, are based on atetrahedral network of atoms comprising silicon and oxygen covalentlybonded to each other. Heat treatment during the assembly process of thefeedthrough structure provides the means by which other elements, suchas alkali and/or alkaline ions, can be introduced into the silica atomicnetwork. When the glass composition formed at the interface is more than60% silica, the atomic network within the glass structure typicallybecomes resistant to reaction with body fluids due to the dense natureof the atomic network structure. However, when the glass compositionformed at the interface is less than about 60%, the glass structure ismore susceptible to atomic structural degradation.

Degradation is generally due to the disruption of the silica atomicnetwork within the glass structure by other elements, such as alkaliand/or alkaline ions, introduced during binder bake out and sintering.These other elements are typically introduced into the feedthroughstructure from additives used within the green alumina tape or the viafill materials, such as the platinum paste, or both. For example, if theadditives in either material make available alkali-metal atoms forexchange with silicon atoms within the silica atomic network, and if theresult is an interface having a silica weight percent below about 60%,then rapid ion exchange of the alkali-metal cations with hydrogen ionsfrom body fluid typically occurs. This results in the formation offunctional hydroxyl, or —OH, groups that are highly reactive in thebody, breaking down and weakening the atomic network structure of theglass phased interface thus increasing the likelihood of a breach in thehermeticity of the feedthrough terminal. Hence, hermetic structurescreated by mating alumina and platinum are not obvious and any inherencyin the bond developed between these two materials does not necessarilyresult in a biocompatible final structure that can sustain hermeticityover the service life of an AIMD.

Once again referring to U.S. Pat. No. 8,043,454 of Jiang et al., insharp contrast to the present invention, Jiang adds between 1-10 percentby weight of niobium pentoxide. Another way to look at this is in thepresent invention, organic binders and solvents are used as opposed toinorganic additives. Additives to the platinum via fill 180 such asdisclosed by Haq may result in unfavorable functionality. For example,the elongate channel-like structures that are actually a result ofadditives like ceramic powder can lower electrical conductivity if theconductivities of these phases are significantly different from theprimary densified material formed. This is discussed in some of theprior art cited. It is very important for human implant applicationsthat the resistivity of the filled via holes be as low as possible. Theinventors have found that adding any ceramic powder to the platinumpaste substantially increases the electrical resistivity of the postsintered via hole. This is a major reason why the inventors have beenworking over a number of years to develop a pure platinum sintered viahole. This is particularly important for AIMDs, such as implantablecardioverter defibrillators. An implantable cardioverter defibrillatornot only senses electrical activity, but it must be able to deliver avery high voltage and high current shock in order to defibrillate thepatient. This means that the entire system, including the leadconductors, the hermetic terminal subassembly via holes, and associatedinternal circuitry must have very low resistance and low impedance sothat a high current can be effectively delivered. Furthermore, and asnoted above, the creation of a glassy-phased structure 184 bonded hasthe potential problem of latent hermetic leaks when exposed to bodyfluid. The present invention resolves this issue.

In the present invention, a post sintered essentially high purityalumina substrate 188 with one or more via holes 185 that pass from anoutside surface of the alumina substrate 188 to an inside surface of thealumina substrate 188 is provided wherein, the via holes 185 comprise anon-toxic and biocompatible post sintered essentially pure platinumfill. There are several differences between the present invention andthe prior art in addition to those specifically discussed in the briefoverview of specific art cited. In the prior art, typically variousadditives are used to modify the alumina ceramic and/or the platinumpaste. In the prior art, at times, it is not even a pure platinum pastethat is used (see Wessendorf column 5, line 29), but rather onecontaining other refractory type materials, such as tungsten or thelike. These additives are used to match the CTE during fabrication. Inother words, these prior art systems go to a lot of effort to match theceramic and metal parts of the system so that cracking or loss ofhermeticity between the alumina substrate 188 and via 186 does not occurover time. Additionally, much of the prior art processes lay down a thinlayer of ceramic tape, then use thick-film screen printing or othermethods to deposit circuit traces and filler for the previouslyfabricated via holes 180. These fillers include tungsten inks and thelike. Then, these individual layers are dried, stacked up and pressed(laminated) into a bar. There are often registration errors andstair-stepping is visible in the cross-sections of such vias 180.

In the present invention, via holes are not formed in individual tapelayers before stack-up. Instead, the alumina ceramic slurry can bethick-cast into tape and then laid down in layers or it may be injected,molded, powder pressed or the like to form a single monolithicstructure. In this state, the alumina ceramic is still in the green andvery pliable due to the organic binders and solvents that have beentemporarily added to the system. It is at this point that via holes 185are drilled therethrough from the outer surface (body fluid side) to aninner surface (AIMD electronic side) of the alumina substrate 188.Because the holes are drilled after formation of the pre-sinteredceramic substrate 188, there is no requirement for registration with theconsequential “stair-stepping” (due to misregistration) that is visiblein cross sections of some prior art structures, for example thosedescribed in the Second Sight patents.

After via holes are formed, the pure platinum paste composition isinjected under pressure or via vacuum into the via holes 185. Thepressure or vacuum is carefully controlled in the present invention sothat the platinum paste is driven intimately along the surface of theinside of the via such that the paste conforms to and creates a mirrorimage of the inner surface of the via in the alumina ceramic and, in sodoing, interconnect with the already tortuous members prevalent inceramic/particulate formation. A mutually conforming interface 191 isthereby formed between the platinum fill and the inside diameter of thevia hole in the ceramic. (See FIG. 42) Drilling is a preferred method offorming the via hole, but these via holes may also be formed bypunching, laser drilling, water cutting or any other equivalent process.

As used herein, the term “essentially high purity alumina” means aluminaceramic with the chemical formula Al₂O₃. “Essentially pure” means thatthe post-sintered ceramic is at least 96% alumina. In a preferredembodiment, the post-sintered ceramic is at least 99% high purityalumina. Prior to sintering, the alumina may be a paste, a slurry orgreen state, and can contain organic solvents and binders. Once theorganic solvents and binders are baked out, the alumina is sinteredbecoming essentially high purity alumina. Similarly, prior to sintering,the platinum paste also contains binders and solvents. The drilled viasof the ceramic insulator are filled with the platinum paste. It is afterthe binders and solvents are baked out at elevated temperature and thensintered that they are substantially removed and an essentially pureplatinum via hole is created.

One is referred to FIG. 5 which is a flow chart illustrating the mainsteps of the process of the present invention. First, an essentiallyhigh purity alumina substrate is formed. The essentially high purityalumina can be formed either through injection molding, green machining,powder pressing 166, by pressing powder into an injection die, or bytape casting and then stacking and laminating individual layers, under apressure ranging from about 1,000 psi to about 5,000 psi at atemperature ranging from about 60° C. to about 85° C. for about 5minutes to about 15 minutes into a bar 168. After formation of the barin step 168, the via holes are formed preferably by drilling through thestructure, however punching, pressing, laser or waterjet operations mayalso be used to form the holes 170. All of the via holes would be filledin step 172 with an essentially pure platinum paste containing organicsolvents and organic binders. Suitable solvents are selected from thegroup of butyl carbitol, cyclohexanone, n-octyl alcohol, ethyleneglycol, terpineol, glycerol, water, and mixtures thereof. Suitablebinders are selected binder from the group of cellulose, celluloseethers, hydroxypropyl cellulose, carboxymethyl cellulose, ethylcellulose, cellulose gum, acrylic resin, polyvinyl alcohol, polyvinylbutyral, poly(ethylene carbonate), poly(propylene carbonate), apoly(alkylene carbonate) having the general formula R—O—C(═O)—O, andmixtures thereof. It should be noted that organic solvents and bindersalso make up a percentage of the green essentially high purity aluminasubstrate.

A further clarification is required here. As used herein, “essentiallypure” means essentially pure post-sintering once the bulk of the bindersand solvents have been baked out in step 174 and/or sintered in step176, both at elevated temperature. Once the binders and solvents havebeen driven out of the system and sintering 176 has occurred, the resultis a solid monolithic high purity alumina substrate 188 with one or morepure platinum via holes 186 extending from an alumina substrate 188outer surface to an inner surface. The outside diameter or the perimeterof the alumina substrate can now be prepared for attaching a ferrule122. In the present invention, the ferrule 122 is attached usingconventional prior art techniques. That is, the outside diameter orperimeter of the sintered alumina substrate 188 is metalized(sputtered). The metallization would typically be in two layers with afirst layer being an adhesion layer 152 and the second layer being awetting layer 150. Then the ferrule is attached to these metalizedceramic layers through a gold brazing process 178 wherein, pure gold isreflowed such that it wets the titanium ferrule and also wets to themetalized surfaces that were previously sputtered onto the aluminaceramic.

The present invention centers around three enabling areas: (1) viapacking with a high solids loading in the paste, (2) compression by theceramic of the metal paste during binder bake out and sintering, and (3)a controlled cool down rate in combination with interfacial bondingsufficient to tolerate coefficient of thermal expansion (CTE) mismatch.

Metal/ceramic compatibility is an important factor in manufacturinghermetic terminals. The difference in CTEs of the metal and ceramic isrecognized as a major parameter in predicting compatibility. The thermalexpansion of metal is generally considerably greater than those ofceramics. For example, at a bakeout temperature of 500° C., the CTE ofalumina is 7.8×10⁻⁶/K and of platinum is 9.6×10⁻⁶/K. Historically, CTEdifferences within 0.5 to 1.0×10⁻⁶/K between the mating metal andceramic materials are adequate to sustain hermetic bonding between thesematerials. However, it is believed differences beyond these limitsprovided at the bake out temperature for the alumina/platinum pair mayproduce sufficient tensile stresses at the interface during cool down tocause spontaneous bonding failure. Hence, given the significantdifference in CTEs, even at a relatively low temperature of 500° C.,achieving a hermetic seal between the platinum metal and alumina ceramicwould not be expected if the difference in CTE between the sinteredalumina and the platinum metal exceeds 0.5 to 1.0×10⁻⁶/K. Rather, thepresent invention achieves a hermetic feedthrough structure through thecontrolled fabrication process parameters of the platinum metal particlesolids loading within the paste, controlled packing of the platinumpaste within the via, and the controlled shrinkage of the aluminasubstrate and platinum via paste through a prescribed co-fire heatingprofile.

In addition, a highly irregular surface at the material interfacebetween the alumina substrate and the platinum metal particles withinthe via provides a mechanical contribution to adherence and robustnessof the hermetic seal. A surface roughness produced by drill bits,sandblasting, gritblasting or chemical etching of the metal substratecan increase the surface area and, in so doing, provide for a strongermechanical attachment along the mutually conformal interface. Applyingthis concept to the alumina/platinum interface therein provides foranother novel aspect of the present invention. Examples of sandblastingand gritblasting media include sand, sodium bicarbonate, walnut shells,alumina particles or other equivalent media.

In the present invention, to achieve sustainable hermeticity, thefollowing is required. Because the CTE of platinum is sufficientlyhigher than the CTE of alumina, it is not theoretically possible foralumina to provide compressive forces on a platinum body in a via.Hence, to overcome the CTE differences between these two materials, theplatinum body in the via must be formed using a paste, a slurry or thelike, having a minimum of 80% solids loading. In one embodiment, thesolids loading of the platinum particles within the paste is 90%. Inanother embodiment, the solids loading of the platinum particles withinthe paste is 95%. In addition, the via must be packed with the platinumpaste to occupy at least 90% of the available space within each viaopening. In an embodiment, the platinum paste is packed within the viaopening to occupy 95% of the space. In another embodiment, the platinumpaste is packed to occupy 99% of the via opening. The shrinkage of thealumina must be no greater than 20% of that of the platinum fill in thevia. In an embodiment, shrinkage is 14%. In another embodiment,shrinkage is 16%.

Furthermore, the assembly is exposed to a controlled co-firing heatingprofile in ambient air that comprises a binder bakeout portion, asintering portion and a cool down portion. A preferred binder bakeout isat a temperature of between 550° C. to 650° C. A more preferred binderbakeout is at a temperature of between 500° C. to 600° C. The sinteringprofile portion is preferably performed at a temperature ranging from1,400° C. to 1,900° C. for up to 6 hours. A preferred sintering profilehas a temperature between 1,500° C. to 1,800° C. A more preferredsintering temperature is between 1,600° C. to 1,700° C. The cool downportion occurs either by turning off the heating chamber and allowingthe chamber to equalize to room temperature or, preferably by, settingthe cool down portion at a rate of up to 5° C./min from the holdtemperature cooled down to about 1,000° C. At 1,000° C., the chamber isallowed to naturally equalize to room temperature. A more preferred cooldown is at a rate of 1° C./min from the hold temperature to about 1,000°C. and then allowing the heating chamber to naturally equalize to roomtemperature. In so doing, the desired outcome of achieving a robusthermetic seal is achieved between the mating materials of the aluminaand platinum. It is noted that these materials have a CTE mismatchbeyond the limits heretofore recognized as adequate for sustainedbonding.

During processing of the platinum fill densities and additionally duringthe densification phase, compression is imparted by the alumina aroundthe platinum within the via due to the shrinkage of the alumina beinggreater than that of the platinum. Furthermore, the platinum issufficiently malleable at this phase to favorably deform by thecompressive forces being applied by the alumina. The combination of theplatinum solids loading, the platinum packing in the via and theshrinkage of the alumina being greater than the platinum fill results inthe platinum taking the shape of the mating alumina surface. The amountof platinum solids loading, its packing percentage within the via andthe malleability of the platinum material all contribute to formation ofa hermetic seal between the platinum and alumina. In addition, thecompressive forces that result from the greater shrinkage of the aluminasubstrate than that of the platinum within the via limit expansion ofthe platinum and force the platinum to deform such that it forms ahermetic seal. Thus an interface between the alumina and platinummaterials that conforms to the respective interface surfaces and resultsin a nearly exact mirror image of the interfacing surfaces is formed,thereby creating a hermetic bond therebetween. This mutually conformalinterface is critical, particularly as researchers studying bondingbetween alumina and platinum believe that any strength in the bondingbetween the alumina and platinum is physical.

As noted earlier, strong bonding between the alumina and the platinum isthe most important factor in achieving sustainable hermeticity infeedthrough terminals for AIMDs. The inventors have learned that theco-fire parameters used to form the hermetic terminals of the presentinvention provide unanticipated, but novel benefit of leveraging thecatalytic nature of platinum, that is, platinum's affinity for certainelements, which enables either direct bonding or formation of aninterfacial layer between the two materials. Analysis of the interfacebetween the alumina and the platinum of this invention disclosed notonly the creation of an intimate knitline, but, in the case of theinterfacial layer, a hermetic structure that exhibits an amorphous layerat the knitline comprising the elements platinum, aluminum, carbon andoxygen that appears to impart resistance to erosion by body fluids. Boththese bonding mechanisms, direct bonding and an amorphous interfaciallayer, offer additional tolerance to the CTE mismatch between these twomaterials.

FIG. 6 now shows a novel wire bond cap 192 has been placed on top of thevia hole 185. In a preferred embodiment, this wire bond cap 192 could beof similar compatible metal, like pure platinum, such that it could beco-fired, to electrically and mechanically connect to the via hole fillmaterial 186. This wire bond pad 192 can be placed on the top side asshown, or the bottom side, not shown, or both sides depending on theapplication and how wires would be routed to an implanted lead, an AIMDconnector-header block, or the like. Referring once again to FIG. 6, thenovel cap 192 can be set into a counter-bore hole as shown or it can beset flush or proud on the top surface of the alumina 188, or anyvariation thereof. Referring once again to FIG. 6, an implantable leadconductor could be connected to a wire bond pad 192 located on the bodyfluid side. In general, the implantable lead conductor or header blockleadwire 118 would have a distal electrode in contact with biologicalcells.

It has been demonstrated that in a normal patient environment, a patientcan be exposed to EMI. This EMI can take many forms, such as that fromcellular telephones, airport radars, microwave ovens, and the like. Anew international standard ISO 14117 has evolved, which includes testsstandards to which cardiac pacemakers and implantable defibrillatorsmust be exposed in order to be qualified by the FDA. There are similarspecifications for cochlear implants and neurostimulators. Accordingly,it is important to provide EMI filtering at the point of lead conductoringress into the interior of the AIMD. It is best to decouple highfrequency interference before it gets inside of the AIMD housing 102.Once inside an AIMD housing 102 the EMI can undesirably cross-couple orre-radiate to sensitive circuits where it can disrupt the properfunctioning of the AIMD. In extreme cases, pacemaker inhibition has beendocumented which is immediately life-threatening for a pacemakerdependent patient. Accordingly, there is a need in the presentinvention, to provide for EMI filtering at the point of implanted leadingress into the implanted medical device housing 102.

FIG. 7 shows an L-shaped wire bond cap 212. In this case, there is ahole in the wire bond cap through which a pin 242 is either laserwelded, brazed or the like 238 to the L-shaped wire bond cap 212. Thispin ideally would be of platinum or similar compatible metal. Thisassembly is co-fired along with the pure platinum via fill 186 so that asolid mechanical and electrical connection is made between the pin 240and the platinum via material 186. There is also a difference in the waythat the interior leadwires 118′ are attached to the feedthroughcapacitor 124. This is a special feedthrough capacitor that isrectangular in shape. The rectangular shape is better understood bylooking at the cross-sectional views shown in FIGS. 8 and 9. FIG. 8 istaken generally along section 8-8 of FIG. 7. FIG. 9 is generally takenfrom section 9-9 of FIG. 7. The view in FIG. 7, therefore, is the endview of a rectangular structure. The active electrodes 134 are broughtout to the sides of the capacitor, which is better illustrated in FIG.8. This allows wire bond pads 246 to be attached to the capacitor.Attachment is done by thermal-setting conductive adhesives, gold braze,high temperature solders, or the like 248. The capacitor ground plateset 136 is terminated at its ends. This is important so that the groundplates 136 do not short to the active electrode plates 134. This makessubsequent attachment of interior leadwires 118′ very easy. Internalleadwires 118′ can be attached to the wire bond pads 246 by thermalsonic bonding, resistance bonding, resistance welding, soldering,thermal-setting conductive adhesives, brazes, or the like, 244.

FIG. 10 illustrates a round quad polar co-fired high purity alumina(Al₂O₃) hermetic terminal subassembly with one or more pure platinumfilled vias 186 of the present invention. Shown are novel L-shaped wirebond pads 250 a through 250 d, which can be co-fired with the pureplatinum via hole fill 186. Since these wire bond pads 250 are on thebody fluid side, it is important that they be non-toxic andbiocompatible. Ideally, they would be of platinum or similar metal thatwas readily co-fired and matched to the CTE of the solid platinum viafill 186.

FIGS. 11 through 14 illustrate alternative shapes for the wire bond pads250 a through 250 d previously illustrated in FIG. 10. Each wire bondpad has one or more respective downwardly extending extrusions 251 inorder to penetrate the via hole platinum paste 186 so that whenco-firing, a solid mechanical and electrical connection is made.

FIG. 15 shows castellations 254 that have been made (into a squareshape) and the corresponding wire bond pad 252 has also been madesquare. This structure would be much more robust during compressingwelding operations during attachment of leadwires 118 where substantialforce is pressed against the wire bond pad. Referring once again to FIG.15, one can see that the wire bond pads 252 have a co-machined orco-formed post 256. This post would slip down into the via hole paste186 and be co-fired. An ideal material for CTE match would, therefore,be a platinum post, however, gold, titanium, tantalum, palladium can allbe used.

FIGS. 16 through 23 show alternative embodiments of the header blockconnector assemblies such as those previously illustrated. FIGS. 16 and17 illustrate stampings, which are ideally of platinum or some othersimilar biocompatible material. They have a hole 264 for convenientreception of leadwire 118 which may then be permanently attached bylaser welding.

FIG. 18 is a sectional view 18-18 taken from FIG. 17 showing thestamping and cross-section.

FIG. 19 is a sectional view showing the stamping of FIGS. 16, 17 and 18co-fired into the novel platinum filled via 186 of the presentinvention.

FIGS. 20 and 21 illustrate another embodiment of stamping 268 b now withfingers 265 that capture the leadwire 118.

FIG. 22 is an alternative embodiment for the header block connectorassembly 268 c, which in this case, has a leadwire 278. The leadwire maybe attached to the bracket 268 c by laser welding or the entire assemblycould be co-machined or even formed by metal injection processes. Inthis case, the leadwire is a platinum or suitable biocompatible materialthat has a CTE that will match that of the platinum filled via 186. Inthis case, the leadwire 278 is co-fired with the platinum filled viamaterial 186 to form a solid electrical and mechanical joint.

FIG. 23 is similar to FIG. 22 except that the header block connectorassembly 268 d has a convenient hole 264 for insertion of the leadwire118 (not shown) where it can be laser welded.

FIG. 24 illustrates a co-fired high purity alumina (Al₂O₃) hermeticterminal subassembly 189 with one or more pure platinum filled vias 186of the present invention, wherein leadwires 118 have been co-fired intothe platinum filled vias 186. In other words, the leadwire 118 isco-fired with the alumina 188 and with the platinum filled via 186, allin one single operation. Leadwires 118 would be routed and connected toimplantable lead conductors or header block connector assemblies, as iswell known in the prior art. As an alternative to a platinum leadwire118, the leadwire 118 may comprise iridium, rhodium, niobium if areducing atmosphere is used or palladium in air if the sinteringtemperature is low enough.

FIG. 25 shows that there are staggered vias 186 and 186′ that are filledwith pure platinum. In this case, platinum leadwires 118 have beenco-fired into the upper vias 186′. As previously stated, these leadwires118 could be routed to implanted leads, to implanted distal electrodesor header block connector assemblies of AIMDs.

FIG. 26 illustrates the co-firing of a novel crimp post 288 into theplatinum filled via 186. Ideally, the crimp post would be of platinum orsimilar biocompatible material, which would have a CTE which closelymatches that of platinum. A leadwire 118 (not shown) would be insertedinto the crimp post and then a mechanical crimping tool would be used toform a mechanical and electrical connection between the walls of thecrimp post and the lead 118. An optional or supplementary laser weldcould also be performed at the point where the leadwire 118 is insertedinto the top of the crimp post 288.

FIG. 27 is similar to FIG. 26 but illustrates a double crimp post. Onthe body fluid side, lead 118 is crimped into the crimp post 290 asshown. On the device inside, a wire 118′ can be inserted and crimpedinto the opposite side 291 of the crimp post 290 to make connection tointernal AIMD circuits. As described before, leadwire 118′ could be aninexpensive copper insulated leadwire or, as in this case, a bareleadwire.

FIG. 28 illustrates a novel method of header block connector assemblyattachment. The header block connector assembly 104 has been completelyprefabricated in accordance with the present invention and has leadwires118 extending down into a novel window 210 of the present invention.Co-molded or co-formed with the header block connector assembly 104 is asupport structure 302. The header block connector assembly 104 is showntilted 90°. There is a co-fired high purity alumina (Al₂O₃) hermeticterminal subassembly 189 with one or more pure platinum filled vias 186of the present invention with novel wire bond post 294. These wire bondposts 294 each have a leadwire protrusion which are inserted into thevia holes and are co-fired with the pure platinum 186. The supportstructure 302 is designed to slip between the two rows of bonding posts294 and provide back support for them. That is, when one pushes againstleadwire 118 very firmly with a resistance welder, this will prevent aplatinum or equivalent post (which are very ductile) from deforming.

FIG. 29 illustrates a different type of post 296 which could be used inFIG. 28. Post 296 has a novel slot 298 which can receive leadwire 118where a laser weld 300 or the like can be performed. The slot can alsobe formed and/or rotated 90 degrees such that it is aligned with thedownward projecting leadwires 118.

FIG. 30 illustrates a co-fired high purity alumina (Al₂O₃) hermeticterminal subassembly 189 with one or more pure platinum filled vias 186of the present invention with a novel crimp post 288 similar to thatpreviously illustrated. In this case, the crimp post 288 is designed toreceive an external leadwire 118 on the body fluid side. On the oppositeside is the nail head structure 306, which could be radiused (notshown). In this case, the crimp post assembly 288 is ideally of platinumor similar material and is co-fired into the platinum filled via 186 inaccordance with the present invention. A feedthrough capacitor 124 isattached using a solder BGA structure 202. It will be obvious to thoseskilled in the art that any of the BGA attachments as illustrated hereincould also be solder dots, solder bumps or dots of thermal-settingconductive adhesives or epoxies, or the like. In a preferred embodiment,material 202 could be of thermal-setting conductive polyimide.

FIGS. 31 through 35 show alternative embodiments of the crimp posts 288.FIG. 31 illustrates the end view of the nail head 306 as previouslyillustrated in FIG. 30. FIGS. 32 through 35 illustrate alternativeembodiments of the nail head structure 288 having respective nail headends 306 a through 306 d.

FIG. 36 is an perspective view of a hermetic seal sub-assembly 101 shownlaser welded 128 into an opening in the housing 102 of an activeimplantable medical device, such as a cardiac pacemaker. The ferrule 122is generally of titanium and in the art, is commonly laser welded 128 asshown to the device housing 102. There is also a hermetic sealsub-assembly 187. The hermetic seal sub-assembly 187 is co-fired alongwith conductive fill material 186 and a conductive insert 402 intoinsulator 188. The conductive insert 402 along with the conductive fillmaterial 186 is all co-fired along with the formation of the aluminaceramic insulator 188. In a preferred embodiment, the conductive fillmaterial 186 would be of substantially pure platinum material and theconductive insert 402 would be of pure platinum or a platinum alloy.Once the insulator sub-assembly 187 has been co-fired, its edges canthen be metallized by sputtering 150, 152 such that the entire perimeterinsulator substrate can be gold-brazed 140 into the insideracetrack-shaped opening of the conductive ferrule 122.

FIG. 37 shows the device side of the hermetic terminal sub-assemblyshown of FIG. 36. FIG. 37 is very similar to FIG. 36 except that theunit has been flipped over so one can see the device side on top.Referring once again to FIG. 37 on the device side, there would beelectrical connections (not shown) to the ends of the conductive insert402 for attachment to appropriate location to AIMD electronic circuits.Referring to FIG. 36, on the body fluid side, there would also beconductive attachments that would connect between the conductive insert402 and/or the conductive fill 186 to various connector locations withinan AIMD header block (not shown). Some AIMDs do not have a header blockand instead have a direct connection from an implanted lead to thehermetic seal conductor. In this case, an implanted lead (not shown)with five conductors, would be connected to the five terminal padlocations 402.

FIG. 38 is taken generally from section 38-38 from FIG. 36 and shows thehermetic seal sub-assembly 101 in cross-sectional view. In FIG. 38, onecan see the sputtered adhesion layer 152 which could consist of niobiumor molybdenum and then followed by sputtering on of a wetting layer 150of titanium or the like. Then gold braze material 140 can be flowed tothe titanium ferrule 122 and to the wetting layer 150 thereby forming arobust, mechanical and hermetically sealed joint. As used herein, theterm hermetic seal means that the hermetic seal sub-assembly, once it'sinstalled in an AIMD housing, would have a helium leak rate of nogreater than 1×10−7 cubic centimeters per second. Referring again toFIG. 38, it is a feature of the present invention that the conductivefill material 186 is conductive from the body fluid side to the deviceside. The co-fired conductive insert, which at least partially fills theconductive via 186 is also conductive. In general, the conductive paste186 has a certain resistivity after firing into the inside of thealumina insulator 188. In the present invention, the resistance from thebody fluid side to the device side can be reduced significantly byadding a conductive insert 402 at least partially through the via holefrom the device side to the body fluid side. In the case of FIG. 38, theconductive insert 402 penetrates all the way from the body fluid side tothe device side and therefore would substantially improve the electricalconductivity between the body fluid and the device side. In anembodiment, the resistance from the body fluid side to the device sidewould be no more than 2 to 10 milliohms.

FIG. 39 is taken from sectional view 39-39 from FIG. 36 giving oneanother view of the gold braze 140, the wetting layer 150 and theadhesion layer 152 that are all attached to the perimeter of theinsulator 188.

Terminals for use in AIMDs comprising a structure co-fired into aconductive filled via for facilitating a wire attachment requirecompliance with the same hermeticity, durability, reliability andlongevity criteria as expected of traditional hermetic terminal options.Achieving this result, however, offers significant challenge. Thechemical, electrical, mechanical, thermal and manufacturing propertiesof the constituents comprising the material system collectivelycontribute to a sustainable AIMD terminal hermeticity. Hence, materialselection, terminal design, assembly and co-firing methods are critical.For example, shrinkage and shrinkage rates may be matched to preventdevelopment of damaging tensile stresses or selectively different tocreate compressive stresses that not only enable sustainable hermeticitybut also support sustainable hermeticity from additional stressesimparted during wire attachment.

In an embodiment of the present invention is directed to mating boundparticulate conductive particles that are suspended within a mixture ofsolvents and binders, i.e., a paste, with a solid conductive structure.The solid conductive structure may be made from the same material as theparticulate material, of a material with properties similar to theparticulate material, or selectively chosen to be different from theparticulate material to elicit a specific outcome, such as to create ahermetic compression terminal. The solid conductive structure may bepretreated to enhance bondability to the paste (e.g., to increasecontact surface area of the solid conductive structure), formability forassembly (e.g., to reduce stresses imparted by working the material toform the solid conductive structure), wire attachment and the like.

Referring once again to FIG. 38, the conductive insert 402 that isembedded within the conductive filled via must result in an assemblythat results in a conductive solid structure embedded within theconductive via, such that the packing of the conductive particulate inconjunction with the conductive solid within it does not alter theloading requirements to achieve the finished occupied space andresultant shrinkage for two reasons: achieving and sustaininghermeticity at the conductive paste/ceramic interface with controlledtensile stress levels or with ceramic shrinkage to result in acompressive terminal that sustains hermeticity and supports wireattachment loads.

FIG. 40 is very similar to FIG. 36 except that in this case, theconductive inserts 402 can be extended a considerable distance above orbelow the entire hermetic seal sub-assembly. For example, conductiveinsert 402 a is extended into the device side. This could be relativelyshort, as shown, or it could be several inches long to make suitableattachment to circuit attachment points. The same thing is true of thebody fluid side as illustrated in conductive insert 402 b, which extendstowards the body fluid side. This could be made long enough to connectall the way to connector block attachment points (not shown). Insert 402c illustrates that the conductive insert could extend upwards into thebody fluid side and also downward into the device side achieving boththe aforementioned functions at the same time.

FIG. 41 is taken generally from sectional view 41-41 from FIG. 40. Thisshows a close-up view of the via filled with the conductive filledmaterial 186 that is disposed and co-fired within the hermetic sealinsulator 188. The conductive insert 402 is shown. Referring once againto FIG. 41, one can see that the surface of the conductive insert 402has been roughened. For example, the solid conductive structure may beannealed, outgassed, plated, plasma etched, chemically etched, abraided,micro bead blasted, grit blasted, solvent cleaned, anodized, and thelike prior to assembling and co-firing. The mating materials may beco-fired utilizing Low Temperature Co-Fired Ceramic (LTCC) or HighTemperature Co-Fired Ceramic (HTCC) methodology, or some combination ofboth. Co-firing may also comprise additional steps, for example but notlimited to, brazing, soldering or use of sacrificial volume materials.

FIG. 42 is taken generally from partial section 42-42 from FIG. 41 andshows the mutually conforming interface between the conductive fillmaterial 186 and the inside surface of the co-fired alumina ceramicinsulator 188. As previously described in U.S. Pat. No. 8,653,384, theentire contents of which are incorporated herein by reference, one willsee that this surface, as shown in FIG. 42, is torturous and mutuallyconforming, meaning that the peaks and valleys of this surface 191 arecompletely filled in by the closely co-bonded and fired conductive fill186. This is very important to form both a physically strong and highlyhermetic seal joint.

FIG. 43 is taken generally from partial section 43-43 from FIG. 41 andillustrates the highly desirable roughened surface 191′ of theconductive insert 402. This roughened surface acts very similar to thatpreviously described in FIG. 42 in that, this gives a place for theconductive fill material 186 to lock in and form a very mechanicallystrong and hermetic bond.

Referring once again to FIG. 42, one can see the interfacial knit line191 that is formed between the co-fired alumina 188 and the conductivefill 186. In FIG. 42, one will notice that it is perfectly acceptablefor the conductive fill to have some closed porosity holes 190 as shown.These can vary in size, as shown in 190′ and 190″. It is very importantin the present invention and is previously described in U.S. Pat. No.8,653,384 that these not be open cells such that a continuous hermeticleak path could be formed.

FIG. 43 shows a close-up of the knit line 191′ that is formed betweenthe conductive fill material 186 and the solid metal of conductiveinsert material 402. One can see that it is highly desirable that thesurface 191′ be rough and that the conductive fill material, uponco-firing, forms a tight bond thereby filling in all the peaks andvalleys along that roughened surface.

FIG. 44 is very similar to FIG. 41 except that the conductive insert 402is surrounded by a plating, a coating or a cladding material 410. Thistype of structure is also known as drawn filled tubing. For example, thecore or the inside of the conductive insert 402 could be of pure silverand the cladding 410 could be MP35N. The advantage of the silver wouldbe extremely high conductivity and the advantage of the cladding wouldbe to completely coat the silver, including particularly the body fluidside, such that the conductive insert was not only conductive, but alsocompletely non-toxic and biocompatible. In one embodiment, it would onlybe necessary to have the biocompatible coating 410 on the body fluidside. Since body fluids cannot enter the hermetically sealed housing ofthe AIMD and it is not important for the device side to have a coating410. In fact, it could be an advantage to enhance solderability or wirebond attachment to not have the cladding 410 on the device side asshown.

FIG. 45 is taken from section 45-45 of FIG. 36 and is very similar toFIG. 38 except that the conductive inserts 402′ have a nail head feature403. This provides a large surface area for which to attach a conductor,such as a lead conductor or a header block conductor by a laser weld orthe like. Referring once again to FIG. 45, this nail head feature couldbe inverted and directed toward the device side. In this case, thiswould facilitate wire bonding, soldering or making connection to circuitboards on the inside of the device (not shown).

FIG. 46 is taken from section 46-46 of FIG. 36 and very similar to FIG.45 which shows a nail head feature 403 on each of the inserts 402″ and402″. Since the diameter of the via with the conductive fill 186 issmaller than the nail head, a two part construction is utilized. It isnot necessary that a metallurgical bond be formed between the top 402″and the bottom 402″ of the conductive pads and conductive insert. Theformula for resistivity is R=ρl/a wherein, ρ is the resistivity, l isthe length of the conductor and a is the cross-sectional area. So aslong as the gap between the top conductive insert 402″ and the bottom ofthe second conductive insert 402′″ is not very great, then theresistivity from top to bottom will be desirably very low.

In the present invention, it is very important that the via consistingof fill material 186 and a solid insert 402 be of extremely lowresistivity as measured from top to bottom. That is, from the body fluidside to the device side. There are a number of reasons for this. In atherapeutic pacing application, such as a cardiac pacemaker or aneurostimulator, pacing pulses pass from the device electronics throughthis filled via 186, 402 to an implanted lead and one or more of itsassociated electrodes. A voltage drop caused by excessive resistance inthe via could not only degrade pacing pulses but it would also bewasteful of precious battery energy. Low resistivity is even morecritical in high voltage pulse applications, such as for implantablecardioverter defibrillators. An ICD must deliver a very fast rise-timehigh voltage shock (above 700 volts) to properly cardiovert afibrillating heart. If the rise-time of the magnitude of the pulse isdegraded, it will not be nearly as effective. In summary, it is aprimary feature of the present invention that a co-fired filled via holebe achieved, which is extremely low in resistance from the device sideto the body fluid side. In a preferred embodiment, this resistance wouldbe less 10 milliohms. In a particularly preferred embodiment, thisresistance would be less than 2 milliohms.

FIG. 47 is similar to FIG. 38 except that the conductive inserts 404 arein the form of hollow tubelets. Again, like all of the conductiveinserts of the present invention, these are co-fired with the conductivepaste 186 and the alumina insulator 188. The crimp posts 404 extend tothe body fluid side to receive wires coming from an AIMD header block orfrom an AIMD implanted lead 412. As shown, the lead conductor 412 isinserted inside the crimp post opening 406 and then a crimp 414 isformed as shown, which makes a solid electrical and mechanicalconnection. This also can be backed up with a laser weld (not shown) toeffect a metallurgical connection as well.

FIG. 48 shows the hermetic terminal assembly with a crimp post 404inverted so one can see the device side. In this case, the crimp postonly partially fills the via hole with the conductive fill. In otherwords, it does not go all the way through from the device side to thebody fluid side. This feature is best shown in FIGS. 49 and 50, which istaken from section 49-49 and 50-50 from FIG. 47. In this case, one cansee that the top and bottom of the conductive fill via 186 has beenenlarged with a counterbore to increase the contact surface area andalso to provide an area for co-firing of the crimp post 404 which has ahollow center 406. It is desirable that the conductive fill is shownmechanically and electrically attached to both the outside diameter 404and the inside diameter 404 of the tube, such that suitable pullstrength is achieved.

FIG. 50 is generally taken from section 50-50 from FIG. 47 and shows across-section right through the center line of the hermetic sealassembly. One can see the cross-section of the crimp tube 406 solidlyembedded in the conductive fill material 186 as shown.

FIG. 51 is very similar to FIG. 49 except in this case, there are crimpposts 404 and 404′ positioned on both the body fluid side and the deviceside. In this way, body fluid side attachments could be made toleadwires or lead conductors and electrical circuit connections can bemade to electronic circuits (not shown) inside of the AND housing.Referring once again to FIG. 51, one can see that on the body fluid sidethat the crimp post 404 would have to be of non-toxic and biocompatiblematerials, such as platinum and the like. However, on the device side,for example, where crimp post 404′ is shown, these could be inexpensiveand non-biocompatible materials, such as copper since they are notexposed to body fluids. Referring once again to FIG. 51, the conductivefill material 186 has a lower conductivity in comparison to the solidmetal crimp post material 406. The long and relatively narrow section ofthe conductive fill via that's between the top and bottom counterborestherefore, is relatively undesirable since it will create resistancethrough the via from the body fluid side to the device side.

Another embodiment is shown in FIG. 52, wherein one can see that thecrimp post 404 passes through a larger diameter conductive fill via 186.In addition, the top crimp post 404 comes very close to touching thebottom crimp post 404′. In this case, the electrical conductivity fromthe body fluid side to the device side is greatly reduced. An optionalconfiguration is shown in FIG. 27 wherein, the crimp post or tube iscontinuous from top to bottom thereby affecting the lowest resistivitypossible.

FIG. 53 is very similar to FIG. 52 except in this case, there is aslit/slot 408 along the edge of the crimp post 404 which allows it to beeasily crushed down onto a leadwire (not shown).

FIG. 54 shows the hermetic seal with the slotted crimp post of FIG. 53inverted.

FIG. 55 is taken from section 55-55 from FIG. 53 showing the slottedcrimp post in side view.

FIG. 56 is taken from section 56-56 from FIG. 53 again showing theslotted 408 crimp post 404.

FIG. 57 is very similar to FIG. 53 except that the crimp post 404 hasdouble slots 408 as shown. Again, this would be to facilitate crimpingor crushing down the tube of a smaller diameter lead conductor (notshown) that would be inserted into the inner diameter 406.

FIG. 58 is the inverted view taken from FIG. 57.

FIG. 59 is taken from section 59-59 from FIG. 57 showing the doubleslotted crimp post 404 in half section.

FIG. 60 is taken from section 60-60 from FIG. 57 right through thecenter of the device, this time going through the center of both slots408.

FIGS. 61 and 61A through 65 and 65A show alternative configurations foreither partial or fully through crimp posts.

FIG. 66 has a single slot 408 in the crimp post 404. This is verysimilar to FIG. 47 except that the crimp post 404 is continuous all theway through the via from the body fluid side to the device side.

FIG. 67 shows the perspective view of FIG. 66 inverted so one call seethe device side. In this case, there is a single slot 408 shown. It willbe understood by those skilled in the art that this could be a doubleslot or even multiple slots to achieve optimal crimping.

FIG. 68 is taken from section 68-68 from FIG. 66 illustrating that theslotted crimp post 404 extends all the way through the conductive filledvia from the body fluid side to the device side. An advantage to thistype of arrangement is that very inexpensive wires can then be used onthe device side. For example, commercially available insulated 415copper wires 413 can be crimped 412 on the device side and routed toconvenient circuit board locations. This is far less expensive thanrunning, for example, platinum wiring inside of a device. Again, insideof a device, noble materials and biocompatibility are not required sincethere is no exposure to body fluid or tissues.

FIG. 69 is taken from section 69-69 from FIG. 67, again illustrating howthe conductive fill 186 penetrates both the outside and the insidediameter of the crimp post 404. This gives the crimp post 404 a greatdeal of mechanical strength particularly in pull or sheer test.

FIGS. 70A through 70F illustrate different top views for the crimp postarrangements previously described. FIG. 70A is a top view of a singleslotted 408 crimp post 404. FIG. 70B is a top view of a double slotted404 crimp post. FIG. 70B could also be formed from two completelyseparate semi-circular pieces of solid metal which are then co-firedinto the conductive fill to form the crimp post structure. FIG. 70Cillustrates that three separate pieces could be used resulting in threeslots 408. FIG. 70D is very similar to FIG. 70C except that in thiscase, there are four pieces. FIG. 70E illustrates a single slot ovalshaped through crimp post whereas, FIG. 70F illustrates that it couldtake on any other shape, such as square, rectangular or the like.

FIG. 71 illustrates that any of the novel hermetic seals of the presentinvention can have a mounted feedthrough capacitor 124. In this case, anelectrical connection 416 is made from each of the feedthrough capacitorcenter holes to each individual crimp post 404, which could be a solder,thermal-setting conductive adhesive or the like. There is also asuitable electrical connection made from the capacitor outside perimetermetallization 419 to the ferrule 122. The electrical connection material420 could be continuous or discontinuous as shown. In a preferredembodiment, the electrical connection 420 would be between the capacitoroutside perimeter ground metallization 419 into gold brazed areas on thehermetic seal ferrule 122, such that no oxides of titanium could buildup in the electrical connection which could preclude proper highfrequency attenuation of the filter.

FIG. 72 illustrates an alternative filter embodiment wherein, a circuitsubstrate 422 has been placed over the five crimp posts 404. There arefive individual MLCC chip capacitors 194, which are mounted to circuittraces that are already pre-printed on the circuit board 422. Again, anelectrical connection would be made from the circuit board via hole endto each of the crimp posts 404. In addition, the capacitors would all beconnected to a ground circuit trace 418 or individually grounded to agold braze area as shown.

Although several embodiments have been described in detail for purposesof illustration, various modifications may be made to each withoutdeparting from the scope and spirit of the invention. Accordingly, theinvention is not to be limited, except as by the appended claims.

What is claimed is:
 1. A method for making a dielectric substrateconfigured for incorporation into a hermetically sealed feedthrough, themethod comprising the steps of: a) forming a green-state dielectricsubstrate with at least one via hole having a via hole volume; b)filling at least 90% of the via hole volume with a platinum-containingpaste, the platinum-containing paste comprising at least 80% platinumparticles mixed with at least one solvent and at least one binder; andc) heating the green-state dielectric substrate and theplatinum-containing paste in the via hole to sinter the dielectricsubstrate and bake-out the solvent and the binder from the paste tothereby provide a platinum material in the via hole in the sintereddielectric substrate, wherein, after sintering, a shrinkage of thedielectric substrate is up to 20% greater than a shrinkage of theplatinum material in the via hole.
 2. The method of claim 1, includingfilling up to 99% of the via hole volume with the platinum-containingpaste.
 3. The method of claim 1, including providing the shrinkage ofthe dielectric substrate after sintering being from about 14% to 20%greater than the shrinkage of the platinum material in the via hole. 4.The method of claim 1, including providing the sintered dielectricsubstrate comprising at least 96% alumina.
 5. The method of claim 1,including selecting the at least one binder from the group of cellulose,cellulose ethers, hydroxypropyl cellulose, carboxymethyl cellulose,ethyl cellulose, cellulose gum, acrylic resin, polyvinyl alcohol,polyvinyl butyral, polyethylene carbonate), poly(propylene carbonate), apoly(alkylene carbonate) having the general formula R—O—C(═O)—O, andmixtures thereof.
 6. The method of claim 1, including selecting the atleast one solvent from the group of butyl carbitol, cyclohexanone,n-octyl alcohol, ethylene glycol, terpineol, glycerol, water, andmixtures thereof.
 7. The method of claim 1, including providing theplatinum-containing paste having, by weight, at least 90% platinumparticles mixed with the at least one solvent and the at least onebinder.
 8. The method of claim 1, including subjecting the green-statedielectric substrate and the platinum-containing paste in the via holeto the following heating protocol: a) a binder/solvent bake-out heatingportion performed at a bake-out temperature ranging from about 400° C.to about 700° C. for a minimum of 4 hours; b) a sintering heatingportion performed at a sintering temperature ranging from about 1,400°C. to about 1,900° C. for up to 6 hours; and c) a cool down portion at acool-down rate of up to 5°/minute from a maximum sintering temperaturedown to about 1,000° C.
 9. The method of claim 8, including allowing thedielectric substrate and the platinum material in the via hole tonaturally cool from about 1,000° C. to room temperature.
 10. The methodof claim 8, including performing the binder/solvent bake-out heatingportion at a bake-out temperature ranging from about 550° C. to about650° C. for a minimum of 4 hours.
 11. The method of claim 8, includingperforming the binder/solvent bake-out heating portion at a bake-outtemperature ranging from about 500° C. to about 600° C. for a minimum of4 hours.
 12. The method of claim 8, including performing the sinteringheating portion at a sintering temperature ranging from about 1,500° C.to about 1,800° C. for up to 6 hours.
 13. The method of claim 8,including performing the sintering heating portion at a sinteringtemperature ranging from about 1,600° C. to about 1,700° C. for up to 6hours.
 14. The method of claim 8, including performing the cool downportion by allowing a heating chamber containing the dielectricsubstrate to naturally equalize from a maximum sintering temperature toroom temperature.
 15. The method of claim 8, including performing thecool down portion at a cool-down rate of up to 1°/minute from a maximumsintering temperature down to about 1,000° C.
 16. A method for making ahermetically sealed feedthrough, the method comprising the steps of: a)providing an alumina substrate, comprising the steps of: i) forming agreen-state alumina substrate with at least one via hole having a viahole volume; ii) filling at least 90% of the via hole volume with aplatinum-containing paste, the platinum-containing paste comprising atleast 80% platinum particles mixed with at least one solvent and atleast one binder; and iii) heating the green-state alumina substrate andthe platinum-containing paste in the via hole to sinter the aluminasubstrate and bake-out the solvent and the binder from the paste tothereby provide a platinum material in the via hole of the sinteredalumina substrate, wherein, after sintering, a shrinkage of the aluminasubstrate is up to 20% greater than a shrinkage of the platinum materialin the via hole; b) providing a ferrule defining a ferrule opening,wherein the ferrule is configured to be attachable to an opening in ahousing of an active implantable medical device (AIMD); c) positioningthe alumina substrate from step a) in the ferrule opening; and d)hermetically sealing the alumina substrate to the ferrule, wherein whenthe ferrule is attached to the opening in the housing of an AIMD, theplatinum material in the alumina substrate via hole provides aconductive pathway extending from an alumina substrate body fluid sideto an alumina substrate device side, the alumina substrate body fluidand device sides residing outside and inside the AIMD housing,respectively.
 17. The method of claim 16, including filling up to 99% ofthe via hole volume with the platinum-containing paste.
 18. The methodof claim 16, including providing the shrinkage of the alumina substrateafter sintering being from about 14% to 20% greater than the shrinkageof the platinum material in the via hole.
 19. The method of claim 16,including providing the sintered alumina substrate comprising at least96% alumina.
 20. The method of claim 16, including providing theplatinum-containing paste having, by weight, at least 90% platinumparticles mixed with the at least one solvent and the at least onebinder.
 21. The method of claim 20, including selecting the at least onebinder from the group of cellulose, cellulose ethers, hydroxypropylcellulose, carboxymethyl cellulose, ethyl cellulose, cellulose gum,acrylic resin, polyvinyl alcohol, polyvinyl butyral, poly(ethylenecarbonate), poly(propylene carbonate), a poly(alkylene carbonate) havingthe general formula R—O—C(═O)—O, and mixtures thereof.
 22. The method ofclaim 20, including selecting the at least one solvent from the group ofbutyl carbitol, cyclohexanone, n-octyl alcohol, ethylene glycol,terpineol, glycerol, water, and mixtures thereof.
 23. The method ofclaim 16, including providing the alumina substrate by subjecting thegreen-state alumina substrate and the platinum-containing paste in thevia hole to the following heating protocol: a) a binder/solvent bake-outheating portion performed at a bake-out temperature ranging from about400° C. to about 700° C. for a minimum of 4 hours; b) a sinteringheating portion performed at a sintering temperature ranging from about1,400° C. to about 1,900° C. for up to 6 hours; and c) a cool downportion at a cool-down rate of up to 5°/minute from a maximum sinteringtemperature down to about 1,000° C.